The present invention relates to an image display system, and more particularly to an image information transmission method in which the resolution, the number of gray scale level, and the rewriting speed for the display are changeable within the screen.
In recent years, an image display apparatus has become thinner and lighter, a flat panel display such as a liquid crystal display, a PDP (Plasma Display Panel), and an EL display (Electroluminescent Display) has rapidly spread, in place of a CRT that was mainly employed for the image display apparatus. Also, the technical development of an FED (Field Emission Display) has also rapidly progressed. Moreover, the display of high definition, high speed moving picture has become requisite, along with the spread of personal computers, DVD, and digital broadcasting. There will be an increasing demand in the future for the higher performance of the image display unit, and particularly, the display of high definition, high speed moving picture. In particular, the liquid crystal display has been greatly expected as a predominant entity of the FPD.
Thus, a method of driving a TFT active matrix that is typical of the conventional method of driving the liquid crystal display will be described below. In driving the TFT active matrix liquid crystal display, a line sequential scanning method is employed, one scanning pulse being applied to each scanning electrode once for each frame time period. One frame time period of about 1/60 seconds is often used, and this pulse is usually applied from the upper side of the panel to the lower side successively at a shifted timing. Accordingly, in a liquid crystal display unit having as many as 1024×768 pixels, 768 gate wires are scanned within one frame, so that the time width of scanning pulse is equal to about 22 μs [=( 1/60)×( 1/768)(seconds)].
On one hand, a liquid crystal driving voltage for driving a liquid crystal with the pixels of one line to which a scanning pulse is applied, is applied simultaneously to the signal electrodes in synchronism with the scanning pulse. At a selected pixel to which a gate pulse is applied, the gate electrode voltage of a TFT connected to the scanning electrode is increased, so that the TFT is placed in on state. At this time, the liquid crystal driving voltage is applied to a display electrode through the source-to-drain of the TFT to charge a pixel capacitance composed of a liquid crystal capacitance formed between the display electrode and an opposite electrode formed on an opposite substrate and a load capacitance in a pixel within a time period of 22 μs as previously mentioned. By repeating this operation, a liquid crystal applied voltage is applied repetitively at every frame time to the pixel capacitance over the entire face of panel.
Since the conventional TFT active matrix driving is performed as in the above operation, the time width of scanning pulse is shorter along with the higher definition and the increasing number of pixels. Namely, it is required to charge the pixel capacitance within a short time period. Also, to cope with the high speed moving pictures, one frame time must be still shortened, in which the time width of scanning pulse is also shorter.
That is, with the conventional driving method for the image display method or the image display unit, it is difficult to cope with an increase in the display frequency that is caused by the higher definition display, due to a signal delay on the wiring, shortage of the writing time into each pixel, and increased scanning frequency.
In a hold luminescence type image display unit such as a liquid crystal display, when the moving picture is displayed, the image quality may be degraded, as described in IEICE (The Institute of Electronics, Information and Communication Engineers) Transaction EID96-4, pp. 19-26 (1996-06). According to this report, since there is inconsistency between a moving picture that is in hold luminescent and the movement of the line of sight pursuing the moving picture, some blur occurs in the moving picture, degrading the display quality of moving picture. To improve the display quality of moving picture, it was reported that there was a method of providing n times the frame frequency. The method of providing n times the frame frequency involves increasing the display frequency in displaying the moving picture clearly on the hold luminescence type image display unit such as the liquid crystal display. However, with the driving method for the image display method or the image display unit that is employed at present, as already described, the increase in display frequency has approached its upper limit.
In order to cope with the high definition display or moving picture display for which there is increasing demand in the future, new materials have been examined to reduce the wiring resistance or wiring capacitance that is a factor of the signal delay on the wiring. Also, to enhance the writing capability into the pixels, instead of the conventional thin film transistor (TFT) using amorphous silicone, the TFT using polysilicone has been put on the market recently.
Moreover, in JP-A-08-006526 specification, there was described a liquid crystal image display unit having means for switching between one line selection and simultaneous selection of plural lines to change the resolution. However, with this technique, the resolution is constant on the line. Also, there was no description for the method of effecting both high definition and high speed display at the same time. Further, in JP-A-09-329807 specification, there was described a liquid crystal image display unit having block selecting means for reducing the consumption power, in which the changed images are only rewritten in a unit of block. However, the high speed moving picture display is difficult to make due to the signal delay on the wiring and the limited writing capability, while displaying the moving picture to be rewritten on the entire screen.
The image transmission from an image control unit (a so-called graphics controller board) for effecting high definition, high speed display to the image display unit is now considered. As an example of the image display unit, taking the conventional liquid crystal display having as many as 1024×768 pixels, with eight bits for each color of red, green and blue (16 million colors) and a frame frequency of 60 Hz, the bit rate is about 1.1 Gbps, which can not be transferred with one data line. Thus, employing 24 data lines, for example, the data is transmitted to a liquid crystal panel at a lower bit rate per line. Accordingly, the image processing of the image control unit, and the transmission between the image control unit and the image display unit become difficult to make, along with the increased number of pixels and the higher frequency corresponding to the high definition and high speed display.
As described above, to make the high definition or high speed moving picture display, it is required to charge the pixel capacitance at a liquid crystal driving voltage within a short time, and a driving method to treat the high definition and high speed moving picture is needed. Further, since the image processing of the image control unit, and the transmission between the image control unit and the image display unit become difficult to make, the driving method and the transmission method capable of displaying the high definition, high speed moving picture that is increasingly demanded in the future must be provided. Also, there is a demand for the image driving method and the transmission method with flexible procedures that can be employed directly even though the wiring material or the capability of active elements is enhanced.
According to the study of human eyes' visual characteristics, when the moving picture is displayed, the image quality can be sufficiently kept even if the definition or the number of gray scale level is not too increased, because the moving picture is being rewritten at high speed. On the other hand, when the still picture is displayed, though there is no need for rewriting at high speed, the high definition display is required to recognize the image quality sufficient.